Combustion Characteristics of Hydrotreated Vegetable Oil-Diesel Blends under EGR and Low Temperature Combustion Conditions

This paper investigates the effects of Hydrotreated vegetable oil (HVO)-diesel blends on combustion characteristics under various ambient oxygen concentrations and ambient temperatures in a constant volume combustion chamber (CVCC). Combustion characteristics were presented in terms of heat release rate, ignition delay and integral heat release. The shadowgraph images of spray combustion were presented for spray development and combustion progress. The experiment was carried out on CVCC under constant injection pressure and energizing time. The synthetic gas with varied oxygen concentrations between three discrete values from 21, 15 and 10 % to simulate EGR on engine conditions. The ambient temperatures were varied at 1100, 900 and 700 K to study the effects of ambient temperatures. Four different fuels were tested: commercial diesel, commercial diesel-HVO blends and HVO with the single-hole injector. The results showed that decreasing ambient oxygen concentration to 10 % resulted in 13.42 % lower heat release rate and 13.89 % lower integral heat release. This also extended ignition delay. Decreasing ambient temperature resulted in longer ignition delay with higher peak heat release rate. Increasing HVO showed 6.43 % shorter ignition delay compare to diesel due to higher cetane number. The shadowgraph images showed that HVO has better evaporation 0.7 to 0.9 ms after injection due to its lower density, viscosity and distillation temperature at T90.